Photographic method for producing a cathode ray tube screen structure

ABSTRACT

A PROCESS FOR PREPARING A LUMINESCENT SCREEN STRUCTURE OF A CATHODE RAY TUBE COMPRISING (1) COATING A SUPPOTING SURFACE SUCH AS THE INNER SURFACE OF THE FACEPLATE OF THE TUBE, WITH A PHOTOSENSITIVE POLYMERIC FILM CONTAINING 0.06 TO 0.50 WEIGHT PART, LIGHT SCATTERING PARTICLES PER PART POLYMERIC MATERIAL, (2) EXPOSING THE FILM TO A LIGHT IMAGE, (3) REMOVING THE STILL SOLUBLE PORTIONS OF THE FILM, (4) OVERCOATING THE RETAINED FILM PORTIONS WITH A LAYER CONTAINING PARTICLES OF SCREEN STRUCTURE MATERIAL (5) AND THEN REMOVING THE RETAINED FILM PORTION AND OVERCOATING THEREON.

United States Patent O 3,623,867 PHOTOGRAPHIC METHOD FOR PRODUCING ACATHODE RAY TUBE SCREEN STRUCTURE Theodore Alexander Saulnier,Lancaster, Pa., assignor to RCA Corporation No Drawing. Filed Oct. 6,1969, Ser. No. 864,197 Int. Cl. G03c /00, 7/06 US. Cl. 96-361 ClaimsABSTRACT OF THE DISCLOSURE A process for preparing a luminescent screenstructure of a cathode ray tube comprising (1) coating a supportingsurface such as the inner surface of the faceplate of the tube, with aphotosensitive polymeric film containing 0.06 to 0.50 weight part, lightscattering particles per part polymeric material,

(2) exposing the film to a light image,

(3) removing the still soluble portions of the film,

(4) overcoating the retained film portions with a layer containingparticles of screen structure material (5) and then removing theretained film portion and overcoating thereon.

BACKGROUND OF THE INVENTION This invention relates to a novel method forpreparing a screen structure for a cathode ray tube and particularly,but not exclusively, to a novel method for preparing a light-absorbingmatrix for a color television picture tube.

Color television picture tubes which include a light-absorbing matrix asa structural part of the luminescent screen have been describedpreviously, for example, in US. Pat. No. 2,842,697 to F. J. Bingley andNo. 3,146,368 to J. P. Fiore et al. These patents describe colortelevision picture tubes of the aperture mask type (also called shadowmask type) in which a light-absorbing matrix is located on the innersurface of the faceplate of the tube. In this structure, the matrix hasa multiplicity of holes therein, each phosphor dot being concentric withone hole in the matrix.

A reverse printing method for preparing a light-absorbing matrix for acathode ray tube is described in patent application Ser. No. 626,752filed Mar. 29, 1967 by Edith E. Mayaud, now Pat. No. 3,358,310, Jan. 26,1971. In a preferred embodiment of that method, the inner surface of theface plate of a cathode ray tube is coated with a film of clearwater-based photosensitive material (typically a dichromate-sensitizedpolyvinyl alcohol). A light image is projected on the film toinsolubilize selected regions of the film. The film is flushed withwater to remove the still soluble regions of the film while retainingthe insolubilized regions in place. Then, the developed film isovercoated with a layer containing particles of light-absorbingmaterial, such as graphite. Finally, the retained film regions areremoved together with the overlying overcoating, while retainingovercoating in the regions previously occupied by removed portions ofthe film. Such a process produces a satisfactory light-absorbing matrix,although further improvements in the process are desirable, particularlyby requiring a shorter exposure time of the photobinder and betterdefinition of the matrix.

The inner surface of the faceplate is usually stippled or otherwisetextured to conceal surface irregularities introduced during themanufacture of the faceplate. A practical problem of practicing theprocess described in the Mayaud application is that the pattern of clearresist on the surface of the faceplate is difficult to inspect visually,especially on a stipped surface. As a result, many faceplates withdefective photobinder patterns or no pattern 3,623,867 Patented Nov. 30,1971 at all are passed to the overcoating step, and must later bereturned for reprocessing.

SUMMARY In the novel process, a support surface is coated with a film ofa photosensitive polymeric material containing 0.06 to 0.50 weight partinert, light-scattering particles per part polymeric material. Theparticles have an average size of about 150 to 5,000 angstroms. The filmis then exposed and developed to produce a polymeric image; the image isovercoated with a composition containing particles of light-absorbing orother screen structure material; and the polymeric image and overlyingcoating are removed as described in the above-identified Mayaud patentapplication. The process may be used to fabricate a lightabsorbingmatrix, or a phosphor pattern, or other screen structure.

Several advantages result from the inclusion of a relatively lowpercentage of inert, light-scattering particles, such as titaniumdioxide, zirconium dioxide, aluminum oxide or silicon oxide, in thecoating composition. The film, both before and after development, has amilky to translucent appearance and thereby may be easily inspectedvisually for defects. It is noteworthy that the loading of particles inthe film is much less than that used for pigmentation or opacificationof film coatings. It is also noteworthy that the presence of theseparticles does not interfere with the exposure tep by dissipating thelight energy. Instead, the preseric e of these particles enhances theeffects of the light by requiring a shorter exposure time and byproducing a polymeric image with better definition and more uniformhardening throughout.

DESCRIPTION OF THE PREFERRED EMBODI- MENTS.EXAMPLE l A novel method forpreparing a light-absorbing matrix on the inner surface of a faceplateof an aperture mask type color television picture tube will now bedescribed. First, the inner surface of a faceplate is cleaned in theusual way as with water, ammonium bifluoride, hydrofluoric acid,detergent, caustic, etc. to remove any foreign matter. Then, the surfaceis coated with a film of photosensitive material containing an amount oftitanium dioxide. In this example, the film is a sensitized polymericmaterial, particularly polyvinyl alcohol containing soluble dichromateions. The film may be produced by depositing on the surface a quantityof an aqueous photobinder solution containing about:

Wt. percent Polyvinyl alcohol 3.42 Titanium dioxide 0.43 Ammoniumdichromate 0.34

Water Balance to The faceplate is rotated and tilted so that thesolution spreads evenly over the surface. During the latter steps of therotation, infrared heat is applied so that the water in the solutionevaporates and a dry film is formed on the surface.

An aperture mask for the faceplate is positioned above the film and theassembly is placed in a lighthouse, which is an apparatus designed toexpose the film on the faceplate by projection of light through themask. A suitable light house is described in US. Pat. No. 2,885,935 toD. W. Epstein et al. In this example, the mask has circular apertureswith a diameter of about 13 mils and a center-to-center spacing betweenapertures of about 28 mils near the center of the mask. The film isexposed for about 8 minutes to light from a 1,000 Watt quartz lamppositioned about 14 inches from the aperture mask.

During the exposure, light from the lamp is passed through a light pipeor collimator and projected through the mask causing beamlets of lightto pass through the apertures in the mask incident upon the film. Theirradiated regions of the film harden; that is, become insoluble inwater. There is a slight enlargement of the exposed areas above the sizeof the beamlet (to about 16 mils) and a graded hardening at the marginsof the exposed areas. The exposure through the mask is repeated three Itimes, each time with the light incident at a slightly different angleso that the beamlets harden the film in groups of three, as in the usualshadow mask screen manufacture. Substantially less exposure time isrequired with the novel process as compared with the prior process inwhich no titanium dioxide was present in the film. In some tests,reductions in exposure time of the order of 35% have been achieved.

Following exposure, the assembly is removed from the lighthouse and themask separated from the faceplate. The exposed coating is subjected toflushing with a forced spray of water for about 30 seconds, after whichthe faceplate is rinsed with Water and dried. At this point in theprocess, the faceplate surface carries an adherent stencil comprised ofopen areas and of dots of hardened polymeric film coated on the surface.The stencil may be inspected visually, and defects may be detected moreeasily due to the presence of the small quantity of titanium dioxide inthe film. With no titanium dioxide present, the film is so thin and sotransparent that visual inspection is difficult.

The stencil is now overcoated with a composition comprised oflight-absorbing particles. In this example, the overcoating is producedby applying to the stencil a slurry containing about 5.0 weight percentof colloidal graphite in water and then drying the overcoating. It isdesirable to include a trace of a wetting agent in the slurry in orderto facilitate the spreading of the graphite slurry over the stencil. Theovercoating is dried thoroughly for about 1.5 minutes with the aid ofinfrared heat. After cooling, the overcoating is well adhered both tothe polymeric dots of the stencil and to the bare faceplate surface,which is the open area of the stencil.

Next, a chemically digestive agent for the polymeric dots is applied tothe overcoating. In this example, the digestive agent is an aqueoussolution containing about 4 weight percent hydrogen peroxide. Thissolution may be applied to the overcoating as a wash or as a spray underpressure. The hydrogen peroxide solution penetrates the overcoating andthe dots, causing the hardened polyvinyl alcohol of the dots to swelland soften. Subsequent flushing with water removes the softened dotstogether with the overlying portions of the overcoating, but leavesbehind that portion of the overcoating which is adhered directly to thesurface in the open areas of the stencil. At this point, the faceplatecarries a black light-absorbing matrix having a multiplicity of circularholes therethrough about 16 mils in diameter. The edges of the patternare relatively smooth as compared with a similar pattern prepared with afilm that is free of titanium dioxide. Generally, the definition of thepattern prepared by the novel method is better than similar patternsprepared with films that do not have added particulate material.

The black, light-absorbing matrix is now rinsed with water and dried forabout 4 minutes with the aid of infrared heat. Then, the faceplate isprocessed in the usual way to deposit red-emitting phosphor dots,greenemitting phosphor dots and blue-emitting phosphor dots about 17mils in diameter over the holes in the matrix which are about 16 mils indiameter by the usual photographic technique using the same aperturemask as the photographic master in the process. The slight enlargementof the phosphor dots over the holes is achieved by the spreading oflight during projection, which may be enhanced by increasing theexposure time of the hardened areas. The completed screen has a matrixwith holes therein and phosphor dots substantially concentric therewith.A suitable process for depositing phosphor dots is described in anarticle entitled, Color-Television Screen- 4 ing by the Slurry Process,by T. A. Saulnier, Jr., in Electrochemical Technology, 4, 2731 (1966).

The luminescent screen may now be processed in the usual way to apply areflective metal layer on top of the phosphor dots and the black matrix.The screen is baked and assembled with the aperture mask into a cathoderay tube in the usual way. A suitable process for filming andaluminizing is described in an article entitled, Emulsion Filming forColor Television Screens, by T. A. Saulnier, Jr., in ElectrochemicalTechnology, 4, 31-34 (1966).

General considerations The particular steps described above in Example 1may be varied within limits and still fall within the scope of theinvention. Obviously, the novel method may be used to produce screenstructures of different materials on other support surfaces, and forpreparing other screen structures than that described in Example 1. Byscreen structure is meant a structure, luminescent or nonluminescent,which is a part of the screen or target of a cathode ray tube. Some ofthe variations in the novel process are described below.

The photosensitive fiIm.The photosensitive film is produced by coating asupport surface, as by dipping, spraying, flow-coating or spin-coating,with a solution of a polymeric binder, a photosensitizer therefor andinert light-scattering particles. The preferred binder is a polyvinylalcohol which may be sensitized with a small amount of ammoniumdichromate, sodium dichromate, potassium dichromate; or a soluble saltof a metal, such as iron or mercury; or with an organic photosensitizerfor a waterbased photosensitive material, such as a diazo compound.

Besides polyvinyl alcohol, other photosensitive or photosensitizablepolymeric materials may be used. Some suitable water-soluble materialswhich can be made photosensitive are proteins such as gelatin, albuminand fish glue; carbohydrates such as gum arabic and starch; andsynthetic materials such as polyvinyl pyrollidone, and certain acrylicacid derivatives. In general, multifunctional water-soluble polymerscontaining reactive groups, such as OH, COOH, NH CO, singly or incombination may be used. Mixtures of these materials may also be used.Some suitable solvent-soluble photosensitive materials are polyvinylmethyl ketone, KPR and KMER (available from Kodak, Rochester, N.Y.)aminated polystyrene, and hydroxy esters of polyacrylates. Water-solublematerials are preferred, at least because there are a large number ofaqueous solutions that can be used in the subsequent step of graphicimage development. Solvent-soluble photosensitive materials are not asreadily attacked by aqueous solutions. Suitable reagents for the graphicimage development of solvent-based photosensitive materials are acids,bases, and commercial strippers.

It is desirable that the photosensitive material form a smooth, unbrokenand uncrazed layer or film since this will produce the sharpest,cleanest graphic images. To this end, it is preferred that thephotobinder by film-forming either directly upon deposition or during aheating step subsequent to deposition. In many systems, the film formingtemperature can be tailored by adjusting the relative proportions ofingredients constituting the photosensitive material.

The inert, light-scattering particles may be of any chemicalcomposition. Titanium dioxide, zirconium dioxide, silicon dioxide andaluminum oxide are preferred examples, although other materials may beused for this purpose. The particles should have an average size ofabout to 5,000 angstrons. There is a preferred size range for eachmaterial. Titanium dioxide is particularly effective in overcoming imagedefinition problems with a coating applied over the irregular strippledsurface of a typical faceplate. Titanium dioxide with an averageparticle size of about 300 angstroms can be used to produce a coatingwith the desirable optical properties. However,

the optimum particle size and agglomerate size have not been determinedat the present time. The very fine particle material mentioned is moreeasily kept in suspension at the low viscosities used in coating thefilm. Aluminum oxide having an average particle size in the range of 150to 550 angstroms, such as Alon marketed by Cabot Corporation, Boston,Mass, may be used. Silicon dioxide having an average particle size inabout the same range, such as Cabosil marketed by Cabot Corporation, maybe used. Combination of two or more particulate materials may be used.

The particle sizes suggested here cover a wide range of commercialmaterials for pigment and give a broad choice. However, agglomerate sizehas a definite effect on the light-scattering properties of theparticles. This can be demonstrated with a normal paint pigment grade oftitanium dioxide where the particle size distribution is nearly ideal. Acommercial pigment sold by Cabot Corporation, Boston, Mass. as RF-30titanium dioxide performs poorly when simply added With stirring to asolution of polyvinyl alcohol. However, the preparation steps for thephotobinder solution disclosed below in Example 3 have given excellentresults.

The mechanisms which produce the improvement in the noxel method are notentirely understood, but they are believed to be related tofine-particle light-scattering within the coating by the particles oraggregates of the added particulate materials. This scattering tends toreduce lateral travel of light through the coating and to enhance theutilization of light in the exposed area where the light is incident.The effect is to produce a more uniform hardening and a better definedimage of the illuminated areas of the film. The incident light isbelieved to be more uniformly diffused and absorbed in the localizedregions of the film.

Where the photobinder is principally a Water-soluble polymer, theresistance of the stencil to the erosive action of the chemicallydigestive agent used in the graphic image development step may beadjusted, if desired, by including in the film a small amount of a lesswatersoluble polymer, which is referred to herein as a filler resin. Forexample, Where the photobinder is principally polyvinyl alcohol, it ispreferred to include a small amount of an acrylate polymer or copolymeras a filler resin. One suitable acrylate formulation that may be used isRhoplex C-72 (marketed by Rohm and Haas, Philadelphia, Pa.), which is anaqueous suspension containing alkyl and aryl acrylates andmethacrylates. Other Rhoplex acrylate formulations may be used. Theproportion of acrylate polymer may be up to about 100% of the proportionof polyvinyl alcohol present in the coating. One suitable photobindersolution which includes a small amount of acrylate polymer is set forthbelow in Example 2.

Sometimes it is convenient to express the ingredients of the photobindersolution as a weight ratio. The weight ratio of inert light-scatteringparticles to polymeric binder should be in the range of 0.06 to 0.50.This is considerably lower than proportions normally used forpigmentation or opacification where the weight ratios are generally 2.0and higher. The Weight ratio of photosensitizer to polymeric bindershould be in the range of about 0.01 to 0.30. The weight ratio of fillerresin to polymeric binder should be in the range of about 0.0 to 1.0.

The photosensitive film may be of the type which is insolubilized whenexposed to energy in the form of rays of either visible or invisiblelight or electrons. Such photosensitive materials are referred to hereinas negativeacting. Instead one may use a photosensitive material of thetype which is solubilized when exposed to radiant energy. This lattertype of photosensitive material is referred to herein aspositive-acting.

The photographic master.Any pattern form may be used as a photographicmaster for exposing the photosensitive film. Thus, conventional silverhalide images may be used either by projection or contact printing. Inthe case of preparing luminescent screens for cathode ray tubes, one mayalso use an electron beam exposure whereby the electron beam traces outthe pattern by conventional scanning techniques without the use of aphotographic master. In other applications, a mask may be used betweenthe electron gun and the screen. In preparing screen structures forcolor television picture tubes of the shadow mask type, it is preferredto use the aperture mask of the tube as a photographic master forexposing the photosensitive coating. In that case, the light source isplaced at three separate locations in order to produce three sepa rateexposures on the coating, each at a different location. Thus, threeholes are produced in the graphic image for each aperture in the mask.Of course, the aperture mask or other master may be used to produce onlyone, or two, or more than three exposures for the same coating. Theshape and size of the apertures in the aperture mask is not critical.

The ph0toexposure.The photosensitive material is exposed to a pattern ofenergy rays in the range and of the type to which the photosensitivematerial is sensitive. Where dichromated polyvinyl alcohol is thephotosensitive material, radiant energy in the form of electrom beams oras light in the blue and ultraviolet range of the spectrum may be used.Where a contact master is used, one may use a flood exposure. Where theexposure is by projection of an image, a small diameter source ispreferred.

Stencil devel0pment.Where a photoresist technique has been used forproducing the stencil, the exposed photosensitive film is developed inthe manner of the use for that material. In the case of dichromatedpolyvinyl alcohol, the development is carried out by flushing thesurface of the film with water or with other suitable solvent for theunexposed, still-soluble photosensitive material. With other films, thesame or other solvents may be used. The development should leave theminimum residue on the bared support surface so as not to interfere withthe subsequent overcoating step.

The 0verc0a!ing.The overcoating may be of any material which is adherentto the support surface. The overcoating may include a pigment orphosphor. Where it is desired to produce a light-absorbing matrix for acathode ray tube, it is preferred to include in the overcoating arelatively high loading of a dark pigment. The pigment is preferablyelemental carbon in the form of carbon black, acetylene black, orgraphite. Other black pigments that may be used are silver sulfide, ironoxide, lead sulfide, ferrites, and manganese dioxide. The pigment may beblack, white or colored. Where it is desired to produce a luminescentstructure, it is preferred to include a relative high loading ofphosphor particles in the overcoatmg. A process of this type forpreparing patterns of phosphor particles is disclosed in U.S. Pat. No.2,840,470 to A. K. Levine.

The overcoating must make a bond to the support surface that will endurethe subsequent processing, such as removing the image stencil anddepositing the phosphor dots. With some materials, such as somecommerciallyavailable dispersions of graphite in water, the graphiteupon drying makes a bond to a glass faceplate which s adequate. Withother materials, it may be necessary to 1nclude a small amount of abinder in the overcoating such that the dry overcoating develops a bondto the support surface through the use of the binder. Colloidal sihca isa satisfactory binder for lamp black and acetylene black. For example,about 10% of a colloidal silica with respect to the percent pigmentpresent produces a strong bond to the glass faceplate, especially wherea small amount of ammonium dichromate is also present. Besides colloidalsilica, alkali silicates may also be used as the binder.

Where a pigment is used for the purpose of making a light-absorbingmatrix for a picture tube of the shadow mask type, the pigment must bedeposited in sulficient density to develop the necessary opacity forthis purpose. In the case of acetylene black and lamp black, the pigmentshould be deposited in a weight of about 0.2 to 2.0 mg./cm. of surfacearea and, preferably, about 1.0 mg./cm. or more in order that suflicientthickness remains after tube processing. Where graphite or otherpigments are used, slightly lower weights are required for achieving thesame opacity in the final graphic image.

The overcoating should also be permeable to and substantially unaffectedby the graphic image developer, which must swell or erode or dissolve atleast apart of the image stencil. Where the overcoating is entirelyparticles, it is necessarily permeable. Where the overcoating contains abinder, the overcoating may be permeable by nature or may be madepermeable by crazing the overcoating. The bond between the supportingsurface and the overcoating is preferably not substantially attacked bythe graphic image developer. When the overcoating-support surface bondis both inert to the attack of the graphic image developer, and isadherent to the surface, it is possible to develop the graphic imageafter softening with a high-pressure spray of water, without anyalteration of the pattern due to localized overdevelopment. If desired,appreciable amounts of organic material may be incorporated in theovercoating.

Graphic image development.-Any substance that dissolves or degrades thepolymeric material of the stencil into soluble, partially-soluble, orvolatile fragments and leaves the overcoating substantially unattackedmay be used for developing the graphic image.

The preferred method for graphic image development is to apply to theovercoating an aqueous solution of an oxidizing agent in a concentrationsufliciently high such that rapid penetration of the overcoating andsoftening of the stencil occur. In the case of stencils of hardenedpolyvinyl alcohol, the stencil softens rapidly with aqueous solutionscontaining between 1 and 35 weight percent hydrogen peroxide. Higherconcentrations may also be used. Instead of hydrogen peroxide solutions,aqueous solutions of the following may also be used: nitric acid, sodiumperoxide, or other alkali peroxides, perchloric acid or alkaliperchlorates, hydroflorous acid, alkali hypochlorites, peracetic acid,alkali borates, alkali perborates, sodium hydroxides and certainenzymes. The graphic image developer solution is chosen so that it willnot substantially decrease the adherence of the matrix overcoating tothe substrate.

The time and temperature for carrying out the graphic image developmentare not critical, especially in view of the fact that they depend onlyon the removal of the polymeric material of the stencil. However, toofast a development may result in disruption of the overcoating, and tooslow a development may result in the weakening of the bond between theovercoating and the support surface. Hence, in each case, the optimumtime and temperature for image development are empirically determined.

Image development may also be carried out with nonaqueous reagents andmixtures of solvents and waterbased reagents.

EXAMPLE 2 Follow the procedure of Example 1 except substitute thefollowing photobinder solution:

This photobinder solution produces a film which is capable 9f printingpatterns with superior resolution, sharp- 8 ness and with a shorterexposure time than an identical formulation which does not containtitanium dioxide. The presence of Rhoplex increases the resistance ofthe stencil to the erosive action of a hydrogen peroxide solution overthe formulation of Example 1.

EXAMPLE 3 Follow the procedure of Example 1 except substitute thefollowing photobinder solution:

This solution is preferably prepared by first preparing a 10 weightpercent dispersion of titanium dioxide containing 0.1 weight percentdispersant. The dispersant is preferably Tamol 731 marketed by Rohm andHaas Co., Philadelphia, Pa. or Noposant K marketed by Nopco ChemicalCo., Newark, NJ. The dispersion is agitated for extended period (30minutes or more) in a high speed blender. A quantity of 10 weightpercent polyvinyl alcohol stock solution is diluted with the remainingwater of the formulation. Then, the required quantity of 10% dispersionis added slowly to the diluted polyvinyl alcohol solution with rapidstirring. Now, the required quantity of a 22.5 weight percent solidsemulsion of Rhoplex C-72 is added slowly with rapid stirring. Finally,the required quantity of a 5 to 10% aqueous ammonium dichromate solution(adjusted to pH 7.0 with ammonium hydroxide) is slowly added with rapidstirring.

This formulation is designed for application by spin coating processover a stippled concave inner surface of a faceplate for a televisionpicture tube. For this purpose, the viscosity is adjusted to about 26centipoises at about 24 C. to provide the desired coating thickness.Other coating techniques and other viscosities may be used.

What is claimed is:

1. In a process for preparing a luminescent screen structure of acathode ray tube, the steps comprising,

(a) coating a support surface with a film of a polymeric material whosesolubility is altered when it is exposed to radiant energy, said filmcontaining 0.06 to 0.50 weight part inert, light-scrattering particlesper part polymeric material, said particles having an average sizeofabout to 5,000 angstroms,

(b) exposing said film to an image in the form of radiant energy untilthe solubility of the irradiated regions thereof are selectivelyaltered, thereby producing in said film regions of greater solubilityand regions of lesser solubility,

(c) removing those regions of said film with greater solubility therebybaring the areas of the support surface underlying said regions ofgreater solubility, While retaining those regions of said film of lessersolubility,

(d) coating said support surface and said retained film regions with acomposition containing particles of screen structure material,

(e) and then removing at least a portion of said retained coated filmregions and the overcoating composition thereon, while retaining theovercoating composition adhering to said support surface.

2. The process defined in claim 1 wherein said screen structure materialis luminescent.

3. The process defined in claim 1 wherein said screen structure materialis nonluminescent and light-absorbing.

4. The process defined in claim 3 including the subsequent step ofdepositing luminescent material on areas of the supporting surfacepreviously occupied by said retained film regions of lesser solubility.

5. A method for producing a luminescent screen structure upon the innersurface of the glass faceplate of a cathode ray tube comprising:

(a) coating said surface with a film of a water-soluble polymericcomposition whose solubility in water is lowered when it is exposed toradiant energy, said film containing 0.06 to 0.50 weight part inert,lightscattering particles per part polymeric material, said particleshaving an average size of about 150 to 5,000 angstroms,

(b) exposing said film to an image in the form of said radiant energyuntil the solubility of the irradiated regions thereof is selectivelylowered, thereby producing in said film regions with greater solubilityand regions with lesser solubility,

(c) flushing said exposed film with water to remove said regions ofgreater ulobdwilityonotit) said regions of greater solubility down tosaid surface while retaining those regions of lesser solubility,

(d) overcoating said surface and said retained regions of lessersolubility with a composition containing particles of screen structurematerial, said overcoatting being permeable to a solution of chemicallydigestive agent for said retained film regions,

(e) applying to said overcoating said solution of chemically digestiveagent for said retained film regions whereby said agent pentrates saidovercoating and softens at least a portion of the retained film regionsthereunder,

(f) and then flushing away said solubilized film regions 10 and theoverlying overcoating composition, while retaining the overcoatingcomposition on said surface.

6. The method defined in claim 5 wherein said screen structure materialis a black, inorganic, particulate material.

7. The method defined in claim 5 wherein said water soluble polymericcomposition is a dichromate-sensitized polyvinyl alcohol.

8. The method defined in claim 7 wherein said inert light-scatteringparticles are of titanium dioxide and said particles of screen structurematerial are of graphite.

9. The process defined in claim 5 wherein said inert, light-scatteringparticles are titanium dioxide, zirconium dioxide, aluminum oxide,silicon oxide, or combinations thereof.

10. The process defined in claim 9 wherein said inert, light-scatteringparticles are of titanium dioxide.

References Cited UNITED STATES PATENTS 5/1967 Mayaud 9636.1 1/1968 Fioreet al. 96-36.1

US. Cl. X.R.

9638.3; ll733.5C, 33.5CM, 33.5CP

Patent No. 3 a 623 867 Dated November 30, 1971 Inventor(s) TheodoreAlexander Saulnier Column 1, line 47 Column 1, line 71 Column 4, line 58Column 8, line 25 Column 9, line 17 (SEAL) Attest:

EDWARD FLFLETCHER, JR. Attesti'ng Officer It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

After "3,358,310" insert -issued- After "a" change "stipped" to--stippled-- After "photobinder" change "by" to After "for" insert an--Remove "said regions of greater s ulobdwilityonotiO" Signed and sealedthis 2nd day of May 1972.

ROBERT GOTTSCHALK Commissioner of Patents FORM PO-IOSO (10-69) USCOMM-DC60376-F'69 a u.s GOVERNMENT PRINTING orrlc: 1969 0-30-354

